#include <iostream>
using namespace std;

typedef long long LL;
const int N = 5e4 + 10;

LL l, n, m;
LL a[N];

LL calc(LL x) // 当跳跃距离为x时，移走的岩石个数
{
    LL ret = 0;
    for(int i = 0; i <= n; i++)
    {
        int j = i + 1;
        while(j <= n && a[j] - a[i] < x) j++;
        ret += j - i - 1;
        i = j - 1;    
    }
    return ret;
}
int main()
{
    cin >> l >> n >> m;
    for(int i = 1; i <= n; i++) cin >> a[i];
    a[n + 1] = l;
    n++;

    LL left = 1, right = l;
    while(left < right)
    {
        LL mid = (right + left + 1) / 2;
        if(calc(mid) <= m) left = mid;
        else right = mid - 1;
    }
    cout << left << endl;
    return 0;
}